Rework README: heiST name, logos, standard sections, badges, showcase, quick start

[KunoVonHagen]

Rework the README for heiST

The following improvements and updates are required for the README:

• Project Name & Logo: Update the README to reflect the new name "heiST" and include the latest valid logos.
• Project Overview: Add a clear, concise description of heiST, including its purpose and main features.
• Code Coverage: Add a badge or transparent statistics showing code coverage of tests.
• Latest Stable Version: Display the latest release version and a badge, if maintained, for clarity.
• Showcase: Add a short demonstration (with images/video/gif if possible) of core features or workflows.
• Quick Start Guide: Provide a step-by-step quick start guide for new users (installation, setup, running, accessing main features).
• Other Standard Sections: Consider including badges contributing guidelines, license, and links to documentation.

Motivation: Improve user onboarding and project maintainability by providing up-to-date and accessible documentation.